This invention relates generally to a method for controlling the extrusion of fluid materials. More particularly, the invention relates to control of the properties of the material being extruded, with or without the physical parameters of the extrusion process, using a twin screw extruder.
Ever since the advent of polymeric materials and the mixing or processing thereof using extrusion techniques, the art has tried to develop methods of controlling the properties of the composition or compound being extruded or the parameters of the extrusion process itself, such as temperature, throughput, etc. These methods ranged early on from simple analysis of the resulting extruded product, then attempting to adjust extrusion conditions to change the characteristics of the resulting product to very sophisticated mathematical methods such as those described by Costin et al. in Polymer Engineering and Science, mid-December, 1982, Vol. 22, No. 17, pp. 1095-1108. Costin et al. describes a method to control a plasticating extruder by running a xe2x80x9csteady state, step, and time-series analysesxe2x80x9d during extrusion, then derived a xe2x80x9ctransfer functionxe2x80x9d for purpose of process control. Specifically, Costin et al. describe a method to generate a transfer function between extruder pressure and the screw speed to regulate extruder pressure by using the screw speed as a manipulated variable. Costin et al. developed the control algorithm from the transfer function generated. Results were obtained by testing the effectiveness of the control in the face of a pressure surges and a disturbance in feed quality.
While such methods have merit, they do not address the need to dynamically control the extrusion process, in order to control the physical properties of the final product, i.e., exercise product and process control xe2x80x9con the flyxe2x80x9d. An object of this invention is to provide a dynamic control method for the product properties of the extrusion process.
This invention provides for an improvement in a process for controlling the properties of a material extruded in a continuous extrusion process. The improvement resides in the application of multiple periodic pulses, as defined herein below, throughout the entire period of the said continuous extrusion process, in order to provide continuous control over the properties of the continuously extruded material.
More particularly, (1) a pulse of known amount of material is added to a steady extrusion process with changes in product properties, (2) dynamic signals generated by a extruder drive and control system are transmitted to data acquisition system signal conditioning front end hardware, which isolates, amplifies and filters the dynamic signals and outputs analog signals, (3) analog signals output by the data acquisition system signal conditioning front end hardware are converted to digital signals, the digital signals are transmitted to a pulse analysis and control computer, which calculates setpoints, which can be transmitted back to the extruder drive and control system or a feed control system used by the extrusion process.